Wireless access systems have been widely deployed to provide various types of communication services such as voice or data. In general, a wireless access system is a multiple access system that supports communication of multiple users by sharing available system resources (a bandwidth, transmission power, etc.) among them. For example, multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a Single Carrier Frequency Division Multiple Access (SC-FDMA) system.
Several position measurement methods have already been used and as examples of the position measurement methods, included are an A-GNSS (Assisted Global Navigation Satellite System) scheme, an E-CID (Enhanced Cell-ID) scheme, an UTDOA (Uplink Time Difference Of Arrival) scheme, etc. Such a method for measuring a position of a user equipment has been used to provide a user with various location-based services (e.g., advertisement, position tracking, emergency communication means, and the like).
However, although the conventional position measurement methods can be commonly applied to outdoor/indoor environments, typical position measurement accuracy is significantly low.
For instance, in the case of the E-CID scheme, its position measurement accuracy is estimated as 50 m in a LOS (Line Of Sight) environment and 150 m in an NLOS (Non-LOS) environment. In addition, an OTDOA scheme, which is based on a PRS, has a limitation in that positing measurement error may exceed 100 m due to eNB synchronization error, multipath propagation error, UE's RSTD measurement quantization error, timing offset estimation error, etc. Moreover, in the case of the A-GNSS scheme, since a GNSS receiver is required, it also has a limitation in that implementation complexity and battery consumption is increased. Thus, the A-GNSS scheme is difficult to be applied to indoor position measurement.
In other words, such position measurement schemes have already been supported by 3GPP UTRA and E-UTRA standards (e.g., LTE Rel-9). However, considering the fact that buildings are recently getting larger and higher, position measurement methods need to be improved to enhance accuracy in in-building positioning.